The objective of the program is to gain increased understanding of the neutral mechanisms which underlie hearing through and integrated series of studies: 1) determination of the mechanical vibratory properties of the basilar and tectorial membranes in the cochlea, using laser interferometry; 2) analysis of the ways in which speech sounds are encoded in the discharges of auditory nerve fibers as revealed by microelectrode recordings; 3) development of a computer simulation model of the peripheral auditory system, including the micromechanical vibrations of the organ of Corti and the electromechanical and transmitter-release characteristics of the hair cells; 4) study of the function and structure of the cochlear nuclear complex by means of intracellular recording and labeling of neurons in vivo, intracellular analysis of membrane and synaptic physiology of cells in vitro, and biochemical and immunocytochemical studies of neurotransmitters; 5) microelectrode studies of binaural interaction in neurons of the superior olivary complex and inferior colliculus, with the aim of understanding the function of these structures in sound localization as well as their postnatal development in normal animals and in animals deprived of sound input to one ear or with unilateral cochlear lesions. Multidisciplinary methods are employed including, in addition to the techniques mentioned above, electron microscopy and reconstruction of neuronal processes by intracellular injection of horseradish peroxidase. Computers are used extensively in controlling auditory stimuli, in analysis of the temporal discharge characteristics of single neurons and in mathematical modeling. The experimental findings will contribute to basic understanding of the auditory system and may also prove useful in the clinical diagnosis and management of hearing disabilities.